U.S. patent number 5,023,987 [Application Number 07/530,432] was granted by the patent office on 1991-06-18 for strato streak flush patch.
This patent grant is currently assigned to The Boeing Company. Invention is credited to Dale E. Hartz, Jerald L. Swanson, Karl J. Wuepper.
United States Patent |
5,023,987 |
Wuepper , et al. |
June 18, 1991 |
Strato streak flush patch
Abstract
A method and apparatus for repairing composite skin structures
from a blind side. The method includes using an elongated patch
with a compression jig to hold the patch in place while the patch
is either bonded in place or fixed in place with countersunk
fasteners or both. The patch, when used on composite materials, is
constructed and positioned so as to have the same anisotropic
load-carrying characteristics as does the material to be repaired.
A blind side repair can be completely made in the field without
requiring extensive facilities.
Inventors: |
Wuepper; Karl J. (King County,
WA), Swanson; Jerald L. (King County, WA), Hartz; Dale
E. (King County, WA) |
Assignee: |
The Boeing Company (Seattle,
WA)
|
Family
ID: |
27017506 |
Appl.
No.: |
07/530,432 |
Filed: |
May 30, 1990 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
401556 |
Aug 28, 1989 |
|
|
|
|
206566 |
Jun 14, 1988 |
|
|
|
|
Current U.S.
Class: |
29/402.11;
156/98; 29/402.12; 29/402.14; 52/514 |
Current CPC
Class: |
B23P
6/00 (20130101); B29C 73/10 (20130101); B64F
5/40 (20170101); B29K 2105/06 (20130101); B29K
2995/0044 (20130101); Y10T 29/49734 (20150115); Y10T
29/49735 (20150115); Y10T 29/49739 (20150115) |
Current International
Class: |
B23P
6/00 (20060101); B29C 73/00 (20060101); B29C
73/10 (20060101); B64F 5/00 (20060101); B23P
006/00 () |
Field of
Search: |
;29/402.09,402.11,402.12,402.13,402.14,402.15,402.16,402.17,525.1,525.2
;114/227,228,229 ;264/36 ;52/514 ;156/94,98 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2401506 |
|
Jul 1975 |
|
DE |
|
320413 |
|
Nov 1971 |
|
SU |
|
Other References
Divisional Application of U.S. Pat. No. 4,820,564 Issued on Apr.
11, 1989 and is a Divisional of U.S. Pat. No. 4,588,626..
|
Primary Examiner: Gorski; Joseph M.
Attorney, Agent or Firm: Seed and Berry
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. application Ser. No.
07/401,556, filed Aug. 28, 1989, now abandoned, which was a
continuation of U.S. Ser. No. 07/206,566, filed June 14, 1988, now
abandoned.
Claims
What is claimed is:
1. A field repair method for forming a structural blind patch in a
sheet of anisotropic load-bearing material having a known
thickness, comprising the steps of:
providing an anisotropic flush patch having a major axis and a
minor axis of substantially different dimensions, a filler portion
having a thickness equal to the thickness of the material to be
patched, and a circumferential backing lip extending from the
perimeter of the filler portion so as to form a circumferential
shoulder therewith;
providing a grasping member extending from the filler portion;
trimming a damaged area of the material to be patched to the same
shape as that of the filler portion, thereby providing a trimmed
area having a major axis and a minor axis;
aligning the major axis of the flush patch with the minor axis of
the trimmed area;
inserting the minor axis of the flush patch through the major axis
of the trimmed area, thereby inserting the patch through the
trimmed area;
aligning the filler portion with the trimmed area after the flush
patch has been inserted so that the trimmed area is flushly filled
by the filler portion, and so that the circumferential shoulder is
closely received by the trimmed area, and so that the backing lip
abuts the material adjacent to the trimmed area;
fixing the backing lip to the material while holding the flush
patch in place with the grasping member; and
removing the grasping member, whereby compressive loads are
transferred across the trimmed area through the filler portion and
tensile loads are transferred across the trimmed area through the
backing lip.
2. The method of claim 1 wherein the sheet of material is a fully
cured composite of reinforcing fibers oriented in preselected
directions and a binding resin, and wherein the flush patch is a
partially cured composite of reinforcing fibers oriented in the
same preselected directions and a partially cured binding
resin.
3. The method of claim 2, including the step of curing the flush
patch in place under temperature and pressure elevated
substantially above ambient temperature and pressure.
4. The method of claim 1 wherein the fixing step includes passing
blind side fasteners into the backing lip from one side of the
material only and wherein the backing lip extends radially at least
approximately four times the diameter of the blind side
fasteners.
5. The method of claim 4 including prior to the trimming step,
positioning a drilling and tracing template, having an interior
tracing guide defining the shape to be trimmed and a drilling guide
for drilling holes for the fasteners, over the damaged area,
whereafter tracing the area to be trimmed using the tracing guide,
removing the template, and removing the traced area.
6. The method of claim 5 including the step of repositioning the
template around the trimmed area after the inserting step.
7. The method of claim 6 including engaging a compression jig
having pulling means for pulling on the grasping member,
compression means for pushing against the material to be patched,
and positioning means for positively repositioning the template
around the trimmed area with the grasping member, the template, and
the material to be patched after repositioning the template.
8. The method of claim 7, including the steps of drilling coaxial
holes through the material to be patched and the backing lip using
the drilling guide, and including the step of positioning and
tightening said blind side fasteners in the holes.
9. The method of claim 8 wherein the fixing step includes bonding
the flush patch to the material to be patched.
10. The method of claim 1 wherein the flush patch has a body
portion integral with the filler portion and the backing lip.
Description
TECHNICAL FIELD
The invention relates to methods and apparatus for forming blind
patches in composite structures.
BACKGROUND OF THE ART
The external panels and/or flight control surfaces of in ground
support aircraft and military aircraft are exposed to various types
of damage ranging from impact to ballistic type damage. This damage
can result in stress concentration fractures, which, if not
repaired, will propagate and grow with use. Typical prior art
methods of repairing such damaged areas in aircraft having metal
skin include the step of positioning a metal patch on the exterior
of the damaged area so as to overlay the damaged area and overlap
the aircraft skin. The patch is then attached to the skin with
fasteners and caulked to prevent leakage. This method is described
in U.S. Pat. No. 4,517,038, to Miller.
It is desirable to use a patch made from the same material as the
aircraft skin. Thus, a metal patch is used for a metal-skinned
aircraft and a composite patch should be used for a
composite-skinned aircraft. However, metallic and composite
materials have different physical properties which result in loads
being transferred through the materials and patches differently.
Metal is isotropic and transfers loads in all directions with equal
facility. Composite structures, however, are typically designed to
be anisotropic and thus distribute loads well in the direction of
the embedded fibrous reinforcing material while transferring loads
in other directions less effectively. Therefore, it is extremely
important when patching composite materials that the patch be
capable of transferring both compressive and tensile loads across
the damaged area in a manner so as to cooperate with the isotropic
properties of the material to be patched.
In addition to the above, it is highly desirable for both
aerodynamic efficiency and the reduction of radar cross section
(RCS) that the patch be flush with the adjacent sheet of material.
The metallic airplane patch disclosed in Miller is not flush. In
addition, a truly flush patch is desirable because the junction
between the patch and the material is not affected as much as a
nonflush patch by aerodynamic loading. This aerodynamic loading can
cause the bond between the patch and the material to loosen such
that water and other external elements could enter the junction
therebetween to the detriment of the bond.
Difficulty has been encountered in providing a blind-side flush
patch in which access to the damaged area is only available from
the outside. Such a repair is very difficult in the field because
the aircraft component (e.g., the wing section) cannot be
disassembled for access to the interior of the wing. Therefore, a
need exists for a field repair method and apparatus for forming a
structural blind patch in a sheet of composite material.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
field repair method for forming a structural bind patch in a sheet
of composite material having a known thickness.
It is also an object of the present invention to provide a method
and apparatus for forming a blind patch which will transfer tensile
and compressive loads in an anisotropic material.
It is yet another object of the present invention to provide a bind
patch which has a low radar cross section and upon which
aerodynamic loading has minimal effect.
It is yet another object of the above invention to achieve the
above objects with a method and apparatus which can be easily
performed and operated in the field without disassembling portions
of an aircraft to be repaired.
The invention achieves these and other objects and advantages which
will become apparent from the description which follows by
providing a flush patch having a major axis and a minor axis of
substantially different dimensions, a filler portion having a
thickness equal to the thickness of the material to be patched, a
grasping member extending from the filler portion, and a
circumferential backing lip extending from the perimeter of the
filler portion so as to form a circumferential shoulder
therewith.
In the preferred embodiment, the damaged area of the aircraft is
trimmed to the same shape as the filler portion. The minor axis of
the flush patch is inserted through the major axis and the
trimmed-out damaged area so that the damaged area is flushly filled
and the filler portion is closely received by the trimmed area.
The damaged area is first trimmed with the aid of a trimming and
drilling template having an inner trim guide of the same shape as
the filler portion. After the damaged area has been traced and
routed out and the patch inserted, the template is replaced around
the trimmed out area and a compression jig is used to grasp the
grasping member and hold the backing lip of the patch firmly behind
the material adjacent to the trimmed-out area. The jig also
positively positions the template around the trimmed-out area so
that drilling guides in the template can be used to drill coaxial
holes through the perimeter of the trimmed-out area and the backing
lip. A bonding material is preferably positioned between the
backing lip and the material, and the edge of the routed area and
the filler portion, so that a weathertight seal is formed. Blind
side fasteners are then positioned through the holes and tightened
to firmly attach the blind side patch to the material to be
repaired. Tensile loads are transferred from one side of the
material to the other through the fasteners and the patch while
compressive loads are therefore transferred from one side of the
material to the other through the filler portion of the patch.
In a composite structure aircraft, the patch itself and the bonding
material are cured under elevated temperature and pressure through
use of a vacuum bag and heating blanket.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometeric view of a wing section showing a damaged
area and an area patched by the method and apparatus of the present
invention.
FIG. 2 is an enlarged isometric view of circled area 2 in FIG. 1
showing tracing and trimming steps of the present method.
FIG. 3 is a cross-sectional view of the blind patch of the present
invention in use with a template and compression jig of the present
invention.
FIG. 4 is a view similar to FIG. 3 showing the jig compressing the
blind patch against the material to be repaired and the template
having been used as a drilling guide.
FIG. 5 is a view similar to FIG. 4 showing a grasping member of the
blind patch being sheared off so that the patch is flushed to the
sheet of material.
FIG. 6 is a diagrammatic, partial elevational view of a curing step
of the present method.
FIG. 7 is an elevational view of an alternate embodiment of the
patch shown in FIGS. 3 through 5.
BEST MODE FOR CARRYING OUT THE INVENTION
An aircraft wing having a skin manufactured from a composite
material, such as carbon fibers aligned in predetermined directions
and an epoxy resin binder, is generally indicated at reference
numeral 10 in FIG. 1. The aircraft skin 12 is shown with a damaged
area 14 and an area 16 which has been patched by the method and
apparatus of the present invention.
Structures made of composite material (or thermoplastic materials)
are easily susceptible to damage, such as the ballistic damage
shown at reference numeral 14. Repair of these materials usually
requires a controlled environment, a long cure time for bonding
procedures, and complicated repair procedures. The inventive method
and apparatus permit repair of external aircraft structures such as
that shown in FIG. 1 from a blind side (access from one side only)
without the complications usually associated with such repairs. The
repair shown at reference numeral 16 is of a true flush-type,
providing aerodynamic smoothness of the outer boundary layer
airflow. The repair also does not substantially change the radar
cross section of the repaired area. The repair procedure is
admirably suited to use in the field.
As shown in FIG. 2, a template 20 is positioned over the damaged
area 14. The template has an interior tracing guide 22 having a
major, or longitudinal, axis 24 larger than its minor, or
transverse, axis 28. The template also has a plurality of guide
bores 30 for drilling coaxial holes through the aircraft skin 12
and the blind patch, as will be described more fully below.
After the damaged area 14 has been traced out, as shown in FIG. 2,
the template 20 is temporarily removed and the damaged area 14
trimmed out by suitable means, such as by the use of a router
32.
After the damaged area has been trimmed out, a blind patch,
generally indicated at reference numeral 40, is positioned through
the trimmed-out area 42. The blind patch is preferably unitary and
is made from the same composite material as is the aircraft skin
12. In particular, the blind patch 40 is preferably formed with a
fabric reinforcement, such as carbon fiber, which has the same
fiber direction and ply lay-up as the aircraft skin 12, such that
the anisotropic load-bearing properties of the patch correspond to
the anisotropic load-bearing properties of the aircraft skin.
The blind patch 40 has a body portion 44 and a filler portion 46
attached to the body portion 44. The filler portion 46 has the same
shape as the interior tracing guide 22 and the same thickness as
the aircraft skin 12. The body portion 44 has a radially extending,
circumferential backing lip 48 extending beyond the perimeter of
the filler portion 46 a distance approximately equal to four times
the diameter of fasteners which will be more fully described
below.
The blind patch 40 also has a nylon bolt 50 which extends upwardly
from the body portion 44 of the patch through the filler portion 46
to provide a grasping member for the blind patch 40. The blind
patch 40 is inserted into the trimmed-out area 42 by holding the
bolt 50 and aligning the major axis of the blind patch 40 with the
minor axis 24 of the trimmed-out area and inserting the minor axis
of the blind patch through the major axis of the trimmed-out area.
After the blind patch 40 has been inserted through this opening,
the patch is aligned, as shown in FIG. 3, so that the filler
portion 46 is closely received by the trimmed-out area 42, and so
that the backing lip 48 abuts the aircraft skin 12, as shown in
FIGS. 4, 5 and 6.
The blind patch 40 and template 20 are maintained in the position
shown in the figures by a compression jig, generally indicated at
reference numeral 60. The compression jig 60 has two cross-arms 62
and 64, each having threaded bores formed at its ends through which
threaded legs 66 extend. The lower ends of the legs 66 terminate in
respective feet 70. Respective wing nuts 74 are fixed to the upper
ends of the threaded legs 66 so as to rotate therewith. Thus,
rotation of the wing nuts 74 in a clockwise direction causes the
feet 70 to extend downwardly. The cross-arms 62 and 64 also have a
central bore (not threaded) which allows passage of the nylon bolt
50 therethrough. A hex nut 76 (separate from the wing nut 74
therebehind) threadably engages the nylon bolt 50 so as to draw the
bolt and the blind patch 40 towards the cross-arms, while the feet
70 tend to urge the cross-arms 62 and 64 away from the aircraft
skin 12. These counteracting forces compress and hold the blind
patch 40 in the position shown in FIG. 4. Template guide pins 68,
extending downwardly from the cross-arms 62 and 64, are provided to
positively position the template 20 with respect to the blind patch
40 and aircraft 12.
As shown in FIG. 4, the guide bores 30 in the template 20 are used
to guide a drill bit (not shown) to drill coaxial holes 78, 80 (see
FIG. 4) in the aircraft skin 12 and circumferential backing lip 48.
With the jig in place, blind side fasteners, such as Composi-lok
II.RTM. blind side fasteners, manufactured by Monogram Aerospace
Fasteners, a Nortec Company, Los Angeles, Calif., can be used. The
backing lip 48 preferably has a radial dimension which is four
times the diameter of the fastener.
The template 20 can now be removed, as shown in FIG. 4 (the
template guide pin 68 can be made vertically movable), prior to the
fasteners being installed, as shown in FIG. 5. If desired, a
binding agent, such as an adhesive film 100 (as shown in FIG. 3),
can be applied to a shoulder formed between the circumferential
backing lip 48 and the perimeter of the filler portion 46 to make
the seal weathertight.
The fasteners 110 are preferably countersunk so that the outer
surface of the blind patch 40 is flush with the skin 12 of the
aircraft. The fasteners shown at the positions of the guide pins 68
are provided by first removing the guide pins 68 from the position
as shown in FIG. 4 and inserting them in holes 78 and 80, already
bored in different locations, so that the drill bit may access
these areas previously occupied by the guide pins.
In a subsequent step, shown in FIG. 5, an upper portion of the
nylon bolt 50 is sheared off at the level of the aircraft 12 so as
to be flush with the outer surface of the patch 40.
In a further step, shown in FIG. 6, the patch 40 and any adhesive
film 100 applied thereto are fully cured in the field. A vacuum bag
130 is positioned over the blind patch 40. The vacuum bag 130 is
sealed to the aircraft skin 12 by a peripheral run of vacuum
sealing tape 132. Beneath the vacuum bag 130 are positioned, in
descending order: breather plies 134, a nonperforated release film
136, bleeder plies 138, a release film 140, and a peel ply 142. All
of the above plies and films are well known to those of skill in
the composite material art. A vacuum probe 144 is positioned so as
to penetrate the vacuum bag 130 and apply a vacuum pressure of
approximately 20 inches of mercury to the patched area. A heating
blanket 146 is positioned on top of the vacuum bag 130 to heat the
blind patch 40 and adjacent area to a temperature of approximately
350.degree. F. for a preferred period of approximately 2 hours. The
temperature of the repaired area is measured by a thermocouple 148
which penetrates the vacuum sealing tape 132 so as to be adjacent
to the repaired area. An insulating blanket 150 is also preferably
positioned above the heating blanket 146 to minimize heat loss to
the environment.
The resulting blind patch 40, as shown in FIG. 1 at reference
numeral 16, is a true flush patch which closely models the
anisotropic load-bearing properties of the surrounding aircraft
skin 12. The patch can be easily applied in the field using the
method described above without having to disassemble the wing to
get at the blind side. Those of ordinary skill in the art will
readily appreciate other modifications and variations of the
invention described above. For example, as shown in FIG. 7, a nylon
bolt 50 may be positioned on the exterior surface of the filler
portion 48 and broken off in the step shown in FIG. 5 rather than
sheared off. The invention, therefore, is not to be limited by the
above description but is to be determined in scope by the claims
which follow.
* * * * *